As long as a driving force is applied to wheels, a walking support vehicle takes a varying course depending on a steering angle of the vehicle. There are three steering systems in that case, i.e., front wheel steering, rear wheel steering and all (four)-wheel steering, which are used in accordance with the velocity of a traveling vehicle and/or the width of a road surface. For safe and effective traveling, front wheel steering may be used in high speed traveling, rear wheel steering in low speed driving, and all-wheel steering in a narrow road driving, respectively. All-wheel steering includes a steering for driving into the garage where the directions of front and rear wheels are turned in a reversed direction, and a steering for driving sideways where front and rear wheels are turned in the same direction, (hereinafter the former steering system is called “driving-into-the-garage steering”, while the latter “driving-sideways steering”, respectively). It is to be noted that most vehicles employ either one of the foregoing steering systems.
According to the existing techniques, no four-wheel vehicles enable turning on the spot, and thus the driving forms of most four-wheel vehicles are back and forth traveling and clockwise/counter-clockwise turnings only. Braking and stopping are realized by holding down a wheel drum or a rim to a disc or a shoe pad. As a means for controlling a steering angle, a manual and mechanical steering, or an electric servo operation using a joystick is available. Also available is a power steering operation that reduces a burden in using a manual power.
Some of conventional vehicles steer four wheels by driving a connecting wire by manual steering, in which steering forms are limited because the directions of the right and left wheels are always kept parallel to each other. Further, since the shaft of the rear wheel itself is rotated in such convention vehicles, the structure thereof becomes too complicated, as is shown in Patent Document 1. Besides, there is also disclosed a traveling vehicle of which the steering system is to direct the front and rear wheels in the same direction or a different direction, as is shown in Patent Document 2, proposing an attitude control based on proportion and integral control actions introduced into signals from a steering angle detector to produce steering directions, thereby driving a steering electric motor. Also, a steering device that controls a steering angle of all wheels delicately using a controller and an exclusive actuator such as a stepping motor or hydraulic cylinder is disclosed in a Patent Document 3. In a Non-Patent document 1, a steering system enabling the omni directional traveling is defined as an independent steering system.
Patent Document 1: Japanese Unexamined Patent Publication No. 09-109970
Patent Document 2: Japanese Unexamined Patent Publication No. 08-272443
Patent Document 3: Japanese Unexamined Patent Publication No. 07-291143
Non Patent Document 1: Makoto Ichikawa “Steering System and Drive Power Transmission in Wheel Shifting Mechanism” P107-112, Volume 13 No. 1 of Journal of RSJ (The Robotics Society of Japan) published in 1995.